1. Field of the Invention
This invention relates to an electron-emitting device, an electron source constituted thereby, and an image forming apparatus such as a display apparatus which is the application thereof, and particularly to a surface conduction electron-emitting device of novel construction, an electron source using the same, and an image forming apparatus such as a display apparatus which is the application thereof.
2. Related Background Art
A surface conduction electron-emitting device utilizing the phenomenon that electron emission is caused by flowing an electric current to electrically conductive film formed on a substrate.
As examples of this surface conduction electron-emitting device, there have been reported one using SnO2 thin film [M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965)], one using Au thin film [G. Ditmmer, Thin Solid Films, 9, 317 (1972)], one using In2O3/SnO2 thin film [M. Hartwell and C. G. Fonsted, IEEE Trans. ED Conf., 519 (1975)], and one using carbon thin film [Hisashi Araki, et al., Vacuum, Vol. 26, No. 1, P.22 (1983)].
In these surface conduction electron-emitting devices, it has been usual to carry out a power supplying process called “forming” on the electrically conductive film to thereby bring about a state in which electron emission occurs before electron emission is effected.
Here, “forming” is to apply a constant voltage or a voltage slowly rising at a rate of e.g. 1 V/min. or so to the opposite ends of the electrically conductive film, flow an electric current to the electrically conductive film, locally destroy, deform or change the quality of the electrically conductive film and bring about an electrically high resistance state to thereby bring about a state in which electron emission occurs.
By this process, a fissure is formed in a portion of the electrically conductive film, and the phenomenon of electron emission is considered to be attributable to the presence of this fissure. Although in what portion the actual electron emission occurs has not been completely elucidated, the fissure and the area around it are in some cases called “on electron-emitting region” for the sake of convenience.
The applicant has already made many propositions regarding the surface conduction electron-emitting device. For example, regarding the above-described “forming”, the applicant discloses in Japanese Patent No. 2,854,385, U.S. Pat. No. 5,470,265 and U.S. Pat. No. 5,578,897 that it is preferable to effect the forming by applying a pulse voltage to electrically conductive film.
Here, the waveform of the pulse voltage may be by any of a method of maintaining the crest value constant as shown in FIG. 5A of the accompanying drawings, and a method of gradually increasing the crest value as shown in FIG. 5B of the accompanying drawings, and can be suitably chosen with the shape and material of the device and the conditions of the forming taken into account.
Also, subsequently to the forming, it has been found that in an atmosphere containing organic substances, a pulse voltage is repetitively applied to the electron-emitting device, whereby both of a current flowing to the device (device current If) and a current resulting from electron emission (emission current Ie) are increased, and this processing is called “activation”.
This processing forms a deposit composed chiefly of carbon on an area including the fissure formed in the electrically conductive film by the “forming”, and the details thereof are disclosed in Japanese Patent Application Laid-Open No. 7-235255.
When the surface conduction electron-emitting device as described above is applied to an image forming apparatus or the like, low power consumption and high luminance are more required.
Accordingly, as the performance of the electron-emitting device, it has come to be required more than even that the proportion of the emission current Ie to the device current If, i.e., the electron emission efficiency, be made higher.
Also, it is a matter of course that it is necessary to prevent a variation in performance with time by electron emission being continued from becoming greater than in the prior art when such an improvement in performance is to be achieved.